It is a problem in the prior art to break a piece or sheet of glass into two or more pieces with a smooth cut so as to lower the time and labor requirements in polishing or edging of the glass. In particular, it is a problem in the art to break glass sheets.
In the prior art devices, impact devices are directly moved into striking engagement with the glass sheet under the score line. This method of breaking glass does not always produce a clean edge, but rather often produces gouges and flaring. This causes the glazier and glass cutter to spend additional time in the finishing of cut edges of the glass.
An example of the foregoing type of glass breaking device is that shown in U.S. Pat. No. 3,169,683. Here, an extension portion 19 acts together with a core 16 as a hammer. The extension 19 has a ball point 20. The support for the hammer is moved across a sheet of glass directly opposite a score line, so that the glass can be broken along the score line. In this patent, the top surface of the glass is scored along a line 41, and the impactor 10 is held against the undersurface of the sheet 40 with the ball point of the hammer directly under the scored line.
In U.S. Pat. No. 3,568,657, a rock-breaking tool is shown having at one end a chisel point and at the other end, a chisel edge. A slide member 26 is provided for providing an impact force to either the chisel or the chisel edge. In this patent, both the chisel point and the chisel edge are relatively sharp, and would damage a sheet of glass rather than breaking the sheet of glass along a score line. The tool of this patent is useful for breaking the object with which it is in contact.
A similar tool is that shown in U.S. Pat. No. 2,475,041, also having a sharpened tip which would break a glass object with which it is in contact, rather than causing a clean break along a score line.
U.S. Pat. No. 4,470,440 shows another impact-producing tool having a sharpened edge. The sharpened edge of this patent is adapted for directly cutting and breaking into a log against which the edge is placed. This type of sharpened edge is not suitable for use with a glass-breaking tool, as is known in the art, since a sharp edge itself produces fractures and breakage of the glass.
Other axial-impact type hand tools are shown in U.S. Pat. Nos. 3,036,482; 3,565,351; and 4,405,005.